Question 100929

Let x=time it takes both to finish the lawn after Erich started to help

Holly mows the lawn at the rate of 1/50 lawn per minute
Erich mows the lawn at the rate of 1/60 lawn per minute

Together they mow the lawn at the rate of (1/50+1/60 )lawn per minute
1/50+1/60: the LCM is 300 so 1/50=6/300 and 1/60=5/300.
So together they mow the lawn at the rate of (6+5)/300 or 11/300 lawn per minute

Now when Holly mowed the lawn for 10 minutes, she finished (1/50)*10 or 1/5 of the lawn so there's 4/5 of the lawn yet to be mowed:

The question now is:  If Holly and Erich can mow at the rate of 11/300 lawn per minute, how long will it take them to mow 4/5 of the lawn.  Our equation is:

(11/300)*x=4/5   multiply both sides by 300

11x=240  divide both sides by 11

x=240/11 or 21.8181818181818 minutes


CK

(11/300)*(240/11)=4/5
240/300=4/5
4/5=4/5

Hope this helps----ptaylor